1. Field of the Invention
The present invention relates to a device for pulling a silicon single crystal, comprising an element, which annularly surrounds the single crystal growing at a crystallization boundary and this element has a face directed at the single crystal. The invention furthermore relates to a method for pulling a silicon single crystal, in which the single crystal is pulled at a pull rate V chosen in such a way that the ratio V/G is equal to the value 1.3*10.sup.-3 cm.sup.2 min.sup.-1 K.sup.-1 .+-.20%, preferably .+-.10%, where is the axial temperature gradient in the region of the crystallization boundary.
2. The Prior Art
German Publication DE-4,414,947 A1, describes silicon semiconductor wafers which are separated from a single crystal as sometimes having a stacking fault ring. The occurrence of a stacking fault ring is closely connected with the pull rate V and the axial temperature gradient G in the region of the crystallization boundary. According to the empirically derived formula V/G=1.3*10.sup.-3 cm.sup.-2 min.sup.-1 K.sup.-1, it is possible to specify a lower pull rate, above which a stacking fault ring just starts to occur.
The prior art furthermore describes that the stacking fault ring causes separate regions within the semiconductor wafer which are characterized by the presence of different types of defects and different defect densities (E. Doxnberger and W. V. Ammon, Journal Of The Electrochemical Society, Vol. 143, No. 5, 1996). This literature reference also discloses that, with the customarily employed pulling method, the temperature gradient in the region of the crystallization boundary is not constant. This is because the temperature gradient changes in the radial direction, when viewed along the longitudinal axis of the crystal.